The present invention relates to magnetic tape cassettes, and more particularly to a magnetic tape cassette of the type in which recording and reproducing operations are carried out with the magnetic tape partially pulled out of the cassette.
A video tape cassette is an example of a magnetic tape cassette of this type. The video tape cassette has tape drawing openings at opposite ends of the cassette, and the magnetic tape is laid over the tape drawing openings so that it can be partially pulled out of the cassette through the tape drawing openings and brought into contact with a rotary head.
This is suitable for high-density signal recording and reproducing operations because the magnetic tape can be brought into contact with the rotary head with high accuracy. However, the above-described magnetic tape cassette still suffers from significant difficulties, which will be described with reference to FIG. 1.
FIG. 1 is a vertical sectional view of a conventional video tape cassette as viewed from the front of the left tape drawing opening 3. Left and right tape drawing openings are formed at both sides of a center opening in the front part of the cassette. In order to control the movement of the magnetic tape T in the thickness direction of the cassette, there are provided a lower rib 4 formed on the lower half case 1, a guide 5 formed integrally with the rib 4 and which has a sliding surface 6 with which the rear side of the magnetic tape makes sliding contact, an upper rib 7 formed on the upper half case 2 confronting the lower rib 4 and having the same function as the lower rib 4, and a cassette case side wall 9 provided on the side of the front surface (the magnetic layer) of the magnetic tape T. These members define the rectangular tape drawing opening 3.
The tape drawing opening 3 is formed during assembly when the upper half case 2 is placed on the lower half case 1. In this operation, the side surface 7b of the upper rib meets the peripheral surface of the guide 5 (the upper portion of the sliding surface 6). Therefore, if there are variations due to molding inaccuracies in the dimensions of the upper and lower half cases 1 and 2, a gap 10 may undesirably be formed between the guide 5 and the side surface 7b.
The movement of the magnetic tape T in the thickness direction of the cassette is controlled by the edge 4a of the lower rib 4 and the edge 7a of the upper rib 7, and the magnetic tape is run with its rear surface in sliding contact with the sliding surface 6. Therefore, sometimes the magnetic tape T may slide into the gap. In addition, for the same reason, the magnetic tape T may be disengaged from the tape extracting device of the magnetic tape recording and reproducing device when it is loaded therein. As a result, the magnetic tape T may be jammed in the device, and possibly damaged.